The following checklist can be used for the basic troubleshooting of noise in mobile audio installations. The key to success is to relax and systematically go through the vehicle. The problem WILL be found. Murphy’s Law states, however, it will be in the last place you look.
1. TO BEGIN: Be sure that system is correctly designed and matched for compatibility.
2. INSPECT VEHICLE: Verify ground from negative battery terminal to fender and/or chassis. Upgrade as needed. This connection must be capable of handling the current of the entire system. ASSUME NOTHING!
3. CHECK VEHICLE ELECTRICAL SYSTEM: Battery, alternator, etc. Make sure your alternator can adequately supply the sound system as well as other vehicle systems (alarm, lighting, etc.) AMPS/VOLTAGE NOT OK: See service technician to have system repaired or upgraded.
4. PROPERLY MOUNT COMPONENTS:
4.1 Isolate from chassis.
4.2 Mount away from vehicle harnesses, computers, etc.
4.3 Do not hesitate to use a factory wiring diagram if needed. DO NOT GUESS!
5. PROPERLY RUN ALL CABLES:
5.1 USE CORRECT GAUGE WIRE.
5.2 Ground all components to a central point or use "ground sniffer" to locate a quiet area.
5.3 Run power and signal cables down opposite sides of vehicle.
5.4 Properly terminate all connections (double check!).
5.5 Use a relay for clean power if needed.
5.6 Use the same gauge wire for power and ground.
5.7 Check signal cables for continuity and repair any open shields or cold solder points.
6. HOOK EVERYTHING UP: Follow the instructions provided with the component and be sure of polarity. Make sure everything is working and set all line levels. If noise exists, please continue...
GENERAL PROCEDURE FOR LEVEL SETTING:
When setting gain levels, always work from the source unit to the amplifiers.Start by checking your L-R balance. Use a CD with test tones (example: 1kHz sine wave).
Alternate method: Use a pink noise track and a real time analyzer set to read dB level. Convert the dB reading to RMS volts using the conversion chart at the end of this checklist.
Connect a Digital Volt Meter (DVM) to each of the RCA outputs of the head unit (set DVM to AC VOLTS). The output voltage should be the same on both channels. If your meter reads peak voltage, multiply the meter reading by .707 to get the RMS voltage.
If the next component is a Line preamp, set the gain controls on the preamp to the maximum voltage required for the inputs of the next component in the signal path (or until just before distortion is heard) and measure the signal with the DVM. Remember…some preamp/line drivers are capable of over 10VRMS output!
Measure and match the output of each component to the maximum recommended input level of the component following it down the signal path to the amplifier(s).
Keep the input level controls (gains) on the amplifiers as low as possible.
7. IGNITION NOISE: Check for noise in each of the following switch positions:
7.1 IGNITION ON, CAR NOT RUNNING: It is possibly related to an Electronic control module, digital dash, or possibly fuel pump. Do not attempt to filter an E.C.M.! Re-route cables away from control unit or fabricate a shield.
7.2 ACCESSORY POSITION, CAR NOT RUNNING (All accessories off): Substitute an isolated signal source (such as a walk-man CD, tape player, or home CD player), if the system plays fine, the head unit needs to be checked.
7.3 ENGINE RUNNING: Make certain no ground loops exist between components (if they do, see next section.).
NOTE: Pulse Width Modulated headlight switches (like some Honds cars use) can cause a whining type of noise when on, verify this type of problem by turning lights on and off while listening for noise. If this is the problem, the headlight switch may need to be replaced with an alternate type.
8. GROUND LOOPS AND/OR RADIATED NOISE EXIST: Check resistance of all ground cables; consider using central point grounding. Resistance needs to be as low as possible (around .2 ohms) on your meters lowest scale. If not, re-do or upgrade cables. If it is not possible to get the resistance’s this low, try to get them all at an equal value (all the same resistance.)
TIP: Use the combination of a DVM and a ground sniffer (plans available from our technical dept.) to find the best ground point. Remove the positive cable from the vehicles’ battery and check resistance’s from:
A. Ground point of all units with connection point on chassis.
B. Connection point on chassis with the negative terminal of the systems battery.
C. Battery negative terminal with the chassis connection point.
Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
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